A refrigeration system employs the law of thermodynamics to remove heat from a chamber by evaporating a liquid refrigerant in an evaporator within the chamber, and condensing the refrigerant outside the chamber in a condenser. A compressor pumps the refrigerant through the system. To operate properly, the pressure of the liquefied refrigerant from the condenser should be reduced until it is below the evaporation points as it enters the evaporator. To regulate the pressure and flow rate as the liquid enters the evaporator, the circuit includes a refrigeration expansion valve which controls pressure and flow rate by regulating the size of an aperture through which the liquid flows, reducing the size of the aperture to reduce the pressure and the flow rate in the tube to the evaporator, and opening the aperture to increase the pressure and the flow rate in the tube. The ideal volume of refrigerant entering the evaporator is dependent upon the temperature and pressure of the refrigerant in the tube leaving the evaporator and, therefore, the expansion valve includes temperature and pressure sensing devices for receiving temperature and pressure readings from the output end of the evaporator. For a refrigeration system to operate efficiently, the expansion valve must maintain a flow of refrigerant through the evaporator such that there is at least some small amount of unevaporated (liquid) refrigerant still present at the outlet of the evaporator, and to the extent that all the liquid refrigerant evaporates before it reaches the outlet of the evaporator, the efficiency of the system is reduced. The servicing of a cooling system, therefore, includes the maintenance of the compressor, the condenser, the evaporator, and the expansion valve.
The system is made of metal parts carefully brazed together because a refrigerant leak in the circuit would ultimately lead to a system failure. The circuits of existing refrigeration systems, therefore, ideally employ the minimum number of brazings, and, in the interest of minimizing the number of brazings, do not always include a sufficient number of ports which could be used by a technician to measure pressure at critical areas within the system such as at the outlet of the evaporator. Consequently, the pressure of the refrigerant leaving the evaporator of a system cannot normally be measured. A technician servicing the system therefore cannot determine whether the expansion valve is operating efficiently without cutting tubes and installing one or more ports through which the pressure in the tubes may be read. The installation of such pressure ports, however, is a time consuming task which, due to the necessity of creating brazed joints, enhances the likelihood of a refrigerant leak. It would be desirable, therefore, to provide an improved expansion valve which allows the pressure within the tube from the evaporator to be monitored without requiring the tubes in the system to be cut.